Gauge comparator test stand



Dec. 25, 1962 T. P. BUCKMAN GAUGE COMPARATOR TEST STAND 2 Sheets-Sheet 1 Filed Oct. 12. 1959 5 7////// nn, ri

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INVENTOR. THOMAS P. BUCKMAN Dec. 25, 1952 Filed Oct. 12, 1959 T. P. BUCKMAN GAUGE COMPARATOR TEST STAND 2 Sheets-Sheet 2 saw 33 c HYDRAULIC SERVICE INVENTOR.

THOMAS E BucKMAN Un d S e a 3,069,891 GAUGE CUMPARATUR TEST STAND Thomas P. Buelnnan, Eaunland, Calih, assignor to Lockheed Aircraft Corporation, Burbank, Calif. Filed @ct. 12, 1959, Ser. No. 345,843

'7 Claims. (Cl. 73-4) testing of the next gauge, or series of similar gauges.

This prior art procedure consumes considerable amount of lost time which, over a period of time, amounts to a large expense item, and proportionally,increases the unit cost of the equipment on which the gauges are installed.

Furthermore, on conventional test stands, to obtain pressures in excess of the pressure derived from the high pressure bottle, a separate booster is required. Of course,

separate units such as a hydraulic test stand, apneumatic test stand, and a. pressure1booster could be utilized. However, not only would the three units be expensive, but bulky, inconvenient, and duplicate the shortcomings of presently known-test stands. t t

In any manufacturing organization that uses hydraulic and pneumatic pressures such asin, missiles, aircraft, electronics, or propellants, serious consequences can result. when any of thepressure measuring unitsare out of calibration. Systems and components dependenton the gauges of the measuring units could becaused to malfunction; personnel couldbe seriously endangered.

Where any gauge .used on a hydraulic system is trans: ferred to. a pneumatic system, any oil retained .in the Bourdon: tube of that gauge could easily'be transferred to the pneumatic regulating mechanisms, Even one drop of oil on the seat of a pneumatic regulating pressure regulator or checkvalve could cause ,the cracking pressure of that regulatign device to: vary sufliciently to cause malfunction of the component, which in a missile could cause flight failure. caused by the vacuum adherence of oil on lapped valve seats, which can olfset a small movement inspring deflection and pressure differentials t Also the contamination of pneumatic high pressure lines with hydraulic oils 3,969,891 Patented Dec. 25, 19%2 It is therefore an object of this invention to provide a high pressure test stand which is available for testing any liquid or pneumatic gauges with one source of pressure and one set of gauges.

Another object of this invention is to provide a high pressure test stand which will eliminate the need for flushing and purifying the lines when testing pneumatic and hydraulic gauges. v I

A further object of this invention is to provide a high pressure test stand utilizing a contamination-free pneumatic booster cylinder which is capable of reaching exceptionally high pressures.

A further object of this invention isto provide a pneumatic booster cylinder in which hydraulic fluid may be used as a source of pressure at one end of the piston and pure dry. gas v may be expelled at the other, uncontaminated by the hydraulic'fluid. I t

A further object of this invention is to provide an accurate pneumatic-hydraulic pressure transfer. chamber of the bag type with a substantially zero differential of pressure. I N

A further object of this invention is to provide atest stand for comparative testing of hydraulic and pneumatic gauges, utilizing a single set of standards indicators, and which eliminates pressure errQI, hysteresis, diffusion and contamination, and relative to prevalent systems reduces maintenance costs and down time.

These and otherrelated objects will be apparent to those familiar with the subject matter as more fullyset forth in the specification and drawings, in which:

FIGURE 1 is adetail View of a horizontal cross section of the booster cylinder; t FIGURE 2 is a detail view of a horizontal crosssection of the pressure transfer chamber; V

FIGURE 3 is a schematic of the comparator test stand, showing the basic pneumatic and hydraulic systems, and

FIGURE 4 is a cross section taken on line 4--4 of FIGURE 2. t t

, Booster1 Cylinder The pneumatic booster cylinder, as more clearly shown in FIGURE 1, comprises a tubulariportion 1,"having This phenomena apparentlyqis always presents the danger of setting up an explosive 7,

mixture. H

The above noted shortcomings, disadvantages and other discrepancies readily apparent from the detailed description herein, are eliminated. bythe present invention which comprises a portable or stationary bench or stand for interconnecting a source of fluid pressure to a standards pressure indicator such as a high fidelity gauge or electronic recorder, a contamination-free booster'cylinder having two floating pistons for boosting critical dry gaspressure, means for connecting a source of hydraulic fluid to one end of the booster cylinder and pneumatic fluid to the other end, a pair of transfer chambers having theouterspace of each chamberconnectedto one of said fluids, means .connecting a liquid fluid to the inner space ofsaid transfer chambers and to said standardspressure C indicator, and means for connecting gauges to be tested the particular standards indicator from the remaining indicators and from each other.

endcaps 2 and 3. Withinthetubular portionor' cylinder are two floating pistons 4 and 5, hydraulic and pneumatic respectively. The pneumatic piston 5 is connectedto the pistonrod e'and forms chamber A, between the piston and end cap 2. Hydraulicpiston 4 is connected 'to piston rod 7 and forms chamber B between the piston and end cap 3. Between the twopistons is a safety chamber C which isfilled with dry gasfrom pneumatic chamber A by meansof check valve 8. Pneumatic piston 5 hasfan internally and laterally expandable type seal, as illustrated. Hydraulic piston 4, ideally, should have an extremely close tolerance, high finish working area from about three-fourths (3A1) to equal the piston area, and

this working area should be preceded by a fairly close tolerance projection of this piston.

In operation, pneumaticpressure is applied to inlet check valve 9, whereupon piston 5 is withdrawn from end cap 2 and pushes oil piston 4 to a 'bottom-of-cycle position against end cap 3. When piston 5 is extended so as piston advances, the relieved segment, or projection, of

the piston enters the pneumatic (gas) cylinder area without touching the cylinder Walls. Simultaneously, the gas piston is pushed ahead of the oil piston by a layer of dry gas which Was injected into safety chamber C through the gas piston check valve during preloading. When the gas piston reaches the end of its stroke, the oil piston is 'adjustably positioned within a few thousandths of an inch from the gas piston. High pressure gas is removed at outlet check valve 11.

To enhance the contamination-proof quality, the seal areas of hydraulic piston 4 are not permitted to contact the areas of the cylinder 1 which are contacted by the pneumatic piston 5. The permissible stroke of hydraulic piston is determined by the travel of pneumatic piston S and the length of the projection on piston 4. Adjustments are made by the stop nuts 1?. on the pneumatic piston rod and similar stop nuts 13 on the hydraulic piston rod. Any vapor or oil that may accumulate in the safety chamber may be bled olf through the needle valve 14 on the side of the cylinder.

The only circumstance in which the pneumatic booster cylinder system could become dangerous would be where sufiicient particles of a hydraulic oil could get into the pneumatic pressure chamber to set up an explosive mixture. The possibility of any such circumstance becomes remote for several reasons. With the practically lapped piston-tO-cylinder fit combined with near zero pressure differential across the seals of both pistons at high pressure, there can never be suflicient particles of vapor getting through to provide an explosive mixture even at pressure high above the maximum operating pressure. Furthermore, in view of the inlet gas pre-load, intermittent slow temperature build up and the high diffusion rate of heat through the cylinder wall, the temperature of the booster cylinder Will barely rise higher than ambient temperature at peak use. These factors, taken with the cyclic bleeding of chamber C through needle valve 14 on the side of the cylinder, assure safe trouble-free, low maintenance operation of the test stand.

Transfer Chamber FIGURE 2 illustrates the preferred construction of the transfer chamber most ideally suited for this invention. This uni-t is comprised of a cylinder 21 and a cylinder cap 22. A cap port 23 leads to the standards gauge, while the cylinder port 23a leads to a hydraulic pump, to the pneumatic high pressure line or other line under test.

Attached to the cap 22 is a bag 22a which nearly fills the cylinder. This bag arrangement is preferably composed of a soft thin-walled metal tube, non diffusible to helium under high pressure. Said tube is formed in such manner as to enable unrestrained deflection under high hydrostatic pressures while allowing free rise of bubbles during the filling procedure. As can be seen by viewing FIGURE 4, this formed shape is appropriately arranged with vertical corrugations that allow the metal tube to expand outwardly or contract inwardly over short deflection distances (up to $010) without creating back pressure, thereby acting within these limitations much like a plastic or rubber tube without their diffusion and deterioration properties. Hysteresis and linearity phenomena that do occur with a soft aluminum tooth paste tube is so immeasurably low as to be of no consequence for normal gauge testing stand uses. At 10,000 p.s.i., for instance, this pressure differential on tubes tested only .0012 of a pound.

One transfer chamber can be used for any number of gauges and at pressures ranging from zero to the maximum capacity of the gauge testing stand. For example, the transfer chambers designed for the subject stand have been tested to 18,000 p.s.i. without leakage, although the maximum operating pressure is 10,000 p.s.i. Two or more transfer chambers can be used for transmitting the pressure of as many gas or liquid pressures as may be required. As an example, one testing stand may be used 4 for testing oxygen, fuel, hydraulic or air gauges Without any danger of explosion or contamination.

It is understood of course that alternatively other plastic or rubber composition materials of the required characteristics may be used, the limiting factor being that the bag material allow no pressure differential, which would inherently limit the accuracy of the gauge and the upper limit of pressure. The apparent reason that the hysteresis or other pressure differential phenomena exists relative to any metallic or semi-rigid means of transmitting hydrostatic pressures is that, with pressures equally distributed on both sides of the membrane, the transmittal is carried through the molecular structure. As stress limits are reached, the new settings create opposing pressure forces. By using thin, strong, pliable plastic material such as polyvinyl chloride, the pressures transmitted within the molecular structure of the plastic create no discernable pressure differential between external and internal liquid or gas media. The factor of upper limit pressure varies among plastics. Generally, polyvinyl chloride is of no use above 7000 p.s.i. This is also true of rubber compounds such as buna. What happens is that the high hydrostatic pressures tend to break down the molecular structure of these substances. Rubber bags as opposed to 0 rings have vast unconfined exposed areas and deterioration is rapid.

Comparative Test Stand Referring now to FIGURE 3 which is a preferred though not limiting embodiment of the invention, the pneumatic supply or source is indicated as a high pressure bottle 31 which is preferably 1000 to 3000 p.s.i. (2000 p.s.i. chosen herein for illustration only). As shown, suitable connections may be provided for a plurality of bottles, as a reserve supply. The pneumatic source is connected to the inlet port of the pneumatic chamber A of the booster cylinder, through inlet check valve 9. From the pneumatic chamber A, and through an outlet check valve 11, a connection is made to the outer space of transfer chamber 32, and also to a pneumatic test outlet 33. The inner space of the transfer chamber is filled with a suitable liquid and connected through suitable valves to the standards pressure indicators 34, 3S and 36, which are separately protected by snubber valves 37, 38 and 39. As indicated, each of the gauges cover different pressure ranges to facilitate in maintaining greater accuracy.

Hydraulic pressure is provided by pump 40', which may be of any preferred design, either pump or flow types. Hydraulic fluid pressure is applied to chamber B of the booster cylinder and to the outer space of transfer chamber 41. A hydraulic test coupling is provided at 4 2 The inner space of transfer chamber 41 is filled with a suitable liquid, which in this case is the same as in the inner space of transfer chamber 32, and connected to the standards indicators, as shown. As shown in FIGURE 3, a relief valve 43 is provided as a return for excessively high pressure hydraulic fluid to the reservoir tank 44.

For automatic and cyclic operation, as the oil piston 4 reaches the apex of its stroke, a microswitch cam 45 located' on the piston rod operates switch S to energize the solenoid valve 46 located in a pneumatic control line. Pressure regulator valve 47 drops the bottle pressure from 2000 p.s.i. to approximately p.s.i., the latter pressure being applied through solenoid valve 46 to the automatic regulator hydraulic valve 43. When the solenoid valve 46 is energized, the regulator valve 43 causes the input of oil into the chamber to be returned back to the reservoir.

A solenoid type valve may be added to the safety chamber C of the booster cylinder to permit vapor or liquid elimination during each cycle. An alternate method is by use of a mechanical leverage arrangement whereby the gas piston rod stop 12 is utilized to actuate the bleed valve each lower cycle of the piston. The solenoid valve is operated by a microswitch, When the oil piston rod reaches the end of its return stroke.

Also at the end of the return stroke, the oil piston rod switch cam 45 operates switch S to de-energize the solenoid valve thereby closing the return line to the reservoir and causing the oil pressure to recycle the booster cylinder pistons.

Therefore, from the foregoing description, it is apparent that low pressure gauges may be tested without operation of the booster cylinder. For this mode of operation the gas pressure flow is from the bottle source 31 through inlet check valve 9, chamber A, outlet check valve 11, to the transfer chamber outer space and to the gauge to be tested. For high pressure operations the gas flow is the same except that the bottle pressure at inlet check valve 9 is raised to the desired pressure by the booster cylinder and is available at the outlet check valve 11.

As suggested above, additional transfer chambers may be added to increase the utility of the test stand. In each case the transfer chamber will be connected between the standards indicator and the gauge test line. It is to be noted that by using the transfer chambers as described herein, the standards indicator lines are essentially a closed system, and therefore separate from the fluids under test consideration. This feature makes possible the testing of pneumatic, hydraulic or fuel gauges with a single set of standards indicators without the normally required procedure of draining, flushing, and purifying the system when a different set of gauges is tested.

While an illustrative embodiment of the invention has been described herein, it is understood that the invention is in no respect limited thereby, but only as defined by the appended claims. For example, the bag 22a of the transfer chamber may be composed of two plastic films one inside the other as shown in FiGURE 2 and secured to the cap by an O ring 24.

What is claimed is:

1. In combination with a high pressure source of pneumatic fluid and a high pressure source of hydraulic fluid, a hydro-pneumatic gas booster cylinder having two opposed floating pistons, means for applying said pneumatic fluid to an inlet port at one end of said cylinder and against one of said pistons, means applying hydraulic fluid to the other end of said cylinder and against the other of said pistons, the forces resulting from said two fluids opposing each other, said pistons and said cylinder forming a safety chamber between said pistons, a first transfer chamber for transmitting pressure uniformly from one fluid to another, means connecting an outlet port on said one end of said cylinder to one side of said transfer chamber, means connecting the other side of said transfer chamber to a standards indicator, means for connecting said outlet port to a gauge for testing, a second transfer chamber connected between said hydraulic fluid and said standards indicator, and means for connecting a gauge for testing to said hydraulic fluid.

2. In combination with a source of pneumatic pressure and a source of hydraulic pressure, a comparative test system comprising a hydraulically operated pneumatic booster cylinder having a pneumatic chamber and a hydraulic chamber, means connecting said pneumatic pressure source to said pneumatic chamber, means connecting said hydraulic pressure source to said hydraulic chamber, means responsive to an increase in hydraulic pressure for increasing the pressure in said pneumatic chamber, means for applying said increased pneumatic pressure to a pneumatic test outlet, a standards indicator, a first Zero pressure differential transfer chamber connected between said pneumatic chamber and said standards indicator, means for connecting a second transfer chamber between said hydraulic pressure source and said standards indicator,

and means for providing cyclic operation of said booster cylinder.

3. A pneumatic pressure booster cylinder comprising a tubular portion, having two endcaps hermetically sealed on said tubular portion, a pneumatic piston arranged within and near one end of said tubular portion, a first piston rod fixed to said pneumatic piston and extending through one of said caps, means for adjusting the operating length of said first piston rod, a hydraulic piston arranged within and near the other end of said tubular portion, a second piston rod fixed to said hydraulic piston and extending through the other of said caps, means for adjusting the length of said second piston rod, said hydraulic piston having a reduced portion on the end of said piston opposite to said end cap, said pistons being so pro portioned as to provide a safety chamber therebetween, means for applying hydraulic pressure between said hydraulic piston and said other end cap, means including an inlet check valve for applying pneumatic pressure be tween said pneumatic piston and said one end cap, and means including an outlet check valve for removing pneumatic pressure from said one end of said tubular portion, said pistons and piston rods being so constructed and arranged that the same inner surfaces of said tubular portion are never contacted by the working areas of both pistons.

4. The pneumatic pressure booster cylinder as defined by claim 3, in which a relief valve is provided in the pneumatic piston to thereby permit one-way passage of pneumatic pressure through said piston to said safety chamber.

5. The booster cylinder as defined by claim 3, in which a needle valve is provided in the side of said tubular porto bleed off air pressure from said safety chamber.

6. A booster cylinder for supplying variable high pneumatic pressure from a low pressure source, comprising a first and second floating piston within said cylinder, said first piston forming a first chamber at one end of said cylinder, said second piston forming a second chamber at the other end of said cylinder, said pistons being so proportioned as to form a third chamber therebetween, relief valve means in said first piston for interconnecting said first chamber and said third chamber, said second piston having a reduced portion extending into said third chamber, means for adjusting the length of travel of said pistons, whereby the areas of said cylinder contacted by said first piston are not permitted to be contacted by said second piston, means for applying pneumatic pressure to said first chamber, means for applying hydraulic pressure to said second chamber, and means for removing pneumatic pressure from said first chamber.

7. In a hydro-pneumatic cylinder for raising the pressure or pneumatic fluids such as air, oxygen, helium and the like, the combination, comprising a hydraulic piston and a pneumatic piston opposing each other in said cylinder and separated by a safety chamber filled with said pneumatic fluid, means for applying said pneumatic fluid against said pneumatic piston to oppose the pressure in said chamber, means including hydraulic pressure for moving said hydraulic piston toward said pneumatic piston whereby the hydraulic piston compresses said pneumatic fluid.

References Cited in the file of this patent UNITED STATES PATENTS 2,478,938 Osterhus Aug. 16, 1949 2,660,890 Fletcher Dec. 1, 1953 2,725,741 Grant Dec. 6, 1955 2,839,086 Engelberger June 17, 1958 2,854,846 Kaderly Oct. 7, 1958 2,914,089 Allinquant Nov. 24, 1959 

